Non-woven support screen for mass transfer devices

Abstract

An improved non-woven support screen for mass transfer devices including a first set of parallel spaced longitudinally extending filaments having a predetermined thickness or diameter and a second set of parallel spaced filaments obliquely arranged relative to the first set of filaments and having a predetermined thickness or diameter approximately 1/2 that of the first set of filaments to provide improved control of membrane distention for minimizing the masking of the membrane surface by preventing excessive distention in one plane, to reduce the volume of body fluid layer in the membrane (low prime), and provide improved mass transfer efficiency while maintaining gentle mixing of the body fluid. Moreover, the velocity gradient of the exchange fluid is enhanced by the limited space provided for the exchange fluid channels to significantly improve the scrubbing action of the exchange fluid on the membrane surface. Advantageously, the larger diameter of the filaments of the first set provides low operating fluid pressure within the membrane channels by allowing selective distention of the membrane.

What is claimed is: 
     
       1. An improved non-woven support screen for mass transfer devices of the type having a support screen and a fluid transfer membrane therein, wherein the improvement comprises: an array of filaments of round cross-sectional area to prevent damage to the membrane including a first set of filaments spaced parallel to one another in a first plane and a second set of filaments spaced parallel to one another in a second plane, said filaments of said first set having centerlines spaced a distance of between about 1.88 to about 2.54 times the spacing between the centerlines of said filaments of said second set, said sets of filaments being affixed to one another at their crossover points and said second set of said filaments being obliquely arranged relative to said first set of filaments, the thickness of the filaments of said second set being between about 0.37 to about 0.67 times the thickness of said filaments of said first set to substantially minimize masking of the membrane by controlling membrane distention.   
     
     
       2. The improved non-woven support screen recited in claim 1, wherein: equal lengths of the support screen include approximately twice as many filaments of said second set as filaments of said first set.   
     
     
       3. The improved non-woven support screen recited in claim 1, wherein: the diameter of said filaments of said second set are about 0.47 times the diameters of said filaments of said first set.   
     
     
       4. The improved non-woven support screen recited in claim 1, wherein: said oblique angle between said sets of filaments is between about 49° to about 55°.   
     
     
       5. The improved non-woven support screen recited in claim 1, wherein: said filaments of said first set have their centerlines spaced from one another a distance of about 2.18 times the spacing between the centerlines of said filaments of said second set.   
     
     
       6. The improved non-woven support screen recited in claim 5, wherein: said filaments of said first set have a diameter of approximately 0.85 MM;   said filaments of said second set have a diameter of approximately 0.40 MM.   
     
     
       7. The improved non-woven support screen recited in claim 6, wherein: said oblique angle between said sets of filaments is about 52°.   
     
     
       8. An improved non-woven support screen for mass transfer devices of the type having a support screen and mass transfer membrane therein, wherein the improvement comprises: an array of filaments of round cross-sectional area to prevent damage to the membrane and including a first set of filaments spaced parallel to one another in a first plane and a second set of filaments spaced parallel to one another in a second plane, said sets of filaments being affixed to one another at their crossover points, said second set of filaments having a diameter of from 0.37 to about 0.67 times the diameter of said first set of filaments, said filaments of said first set having their centerlines spaced from one another a distance of between about 1.88 to about 2.54 times the spacing between the centerlines of the filaments of said second set, and said second set of filaments being biased at an angle of between about 49° to about 55° relative to said first set of filaments, said first and second filaments coacting with the membrane to control membrane distention to substantially minimize masking of the membrane and enable the membrane to assume a thin layer configuration to thereby control the volume of the membrane.   
     
     
       9. The improved non-woven support screen recited in claim 8, wherein: said filaments of said first set have a diameter of approximately 0.85 MM and said filaments of said second set have a diameter of approximately 0.40 MM;   said filaments of said first set have their centerlines spaced from one another about 2.18 times the spacing between the centerlines of the filaments of said second set; and   the angle between said first and second filaments is about 52°.